Fatigue behaviour of notched specimens of friction stir welded aluminium alloy 6063-T6

Notwithstanding the widespread interest in the possibilities offered by friction stir welding (FSW), data concerning its mechanical behaviour is still needed. Due to design constraints, friction stir welded components may include notches in the weldment (friction stirred material), and there is a lack of information on the fatigue behaviour of the weldment in those conditions. In this work the influence of FSW on the fatigue life of specimens of aluminium alloy 6063-T6, containing notches in the thermo-mechanically affected zone was studied. For this purpose, welded and unwelded notched specimens were fatigue tested under load control at different stress levels. Compared to base material specimens, FSW specimens were found to have longer fatigue lives but generally of the same order of magnitude. The work included hardness, tensile and fatigue tests, and the finite element method analysis of the stress and strain distribution. Microstructure examination and microhardness measurements were performed, and in order to identify welding defects and fracture surface features a scanning electron microscopy analysis was carried out. The notch-strain analysis was used for approximate modelling of the fatigue behaviour observed.